Technical Field
The present invention relates to a liquid jet unit that ejects liquid droplets onto a recording medium to perform recording, and particularly to a circulation type liquid jet unit and a liquid jet apparatus using the same.
Background Information
Recently, there has been used a liquid jet head using an ink jet system that ejects ink droplets onto a recording paper or the like to record characters or figures thereon, or ejects a liquid material onto the surface of an element substrate to form a functional thin film thereon. In the ink jet system, ink or a liquid material is guided from a liquid tank into a channel of a liquid jet head through a supply path, and pressure is applied to liquid filled in the channel to thereby eject the liquid from a nozzle that communicates with the channel. When ejecting liquid, characters or figures are recorded, or a functional thin film having a predetermined shape is formed by moving the liquid jet head or a recording medium.
As liquid jet apparatuses of this type, a liquid jet apparatus that circulates liquid to be supplied to a liquid jet head is widely used. By circulating liquid, it is possible to prevent the occurrence of ejection failure caused by dust or air bubbles accumulated in the liquid jet head, and also possible to constantly supply fresh liquid to the liquid jet head. As a result, deterioration of the recording quality caused by the increase in liquid viscosity can be prevented.
JP 5-330073 A describes a circulation system in which ink is circulated between a recording head unit and an ink tank. An outward ink tube and a return ink tube are placed between the ink tank and the recording head unit. A pump is placed in the outward ink tube at the side near the ink tank. The pump pressure-feeds ink inside the ink tank to the recording head unit, and circulates ink between the ink tank and the recording head unit. With this configuration, air bubbles and ink having increased viscosity (hereinbelow, simply referred to as “viscosity-increased ink”) remaining inside the tube and the recording head unit are collected into the ink tank to be removed.
JP 6-183024 A describes an ink jet recording apparatus in which an ink circulation path is constructed. The ink circulation path is connected from a recovery pump as an ink pressure-feeding unit to an ink inflow port of a recording head via a first circulation tube. Further, the ink circulation path is connected from an ink outflow port of the recording head to the recovery pump via a second circulation tube and an ink supply tank. In addition, a main tank for replenishing the ink supply tank with ink is connected to the ink circulation path. The main tank and the first circulation tube of the ink circulation path are connected to each other via a replenishing tube on which a rectification valve for replenishing is disposed.
Ink is circulated in the following manner. Ink supplied from the ink supply tank is pressure-fed to the first circulation tube by the recovery pump, and flows into a common liquid chamber of the recording head. Then, a part of the pressure-fed ink is ejected along with the operation of the recording head, and the rest part thereof is returned to the ink supply tank via the second circulation tube. Since the rectification valve for replenishing is interposed between the main tank and the first circulation tube, ink does not flow into the main tank from the first circulation tube. When ink stored in the ink supply tank has been consumed, the feeding direction of ink by the recovery pump is reversed. Accordingly, ink is sucked into the first circulation tube from the main tank, and the ink supply tank is replenished with the ink via the recovery pump.
FIG. 12 is a diagram of an ink flow path of an ink jet recording apparatus described in JP 9-104120 A. JP 9-104120 A describes the operation and configuration for reducing the increased viscosity of ink at an ejection port 120 of the ink jet head 111. In the ink flow path, a circulation path is formed by an ink circulation pump 113, a tube 117b, a joint 117c, a tube 117a, a common liquid chamber 112 of the ink jet head 111, and a collection tube 116. Further, ink supplied from a main ink tank 115 is pressure-fed to the joint 117c via the tube 119 by an ink supply pump 114 so as to be supplied to the circulation path.
When the viscosity of ink at the ejection port 120 increases, the ink circulation pump 113 is operated to collect the viscosity-increased ink through the collection tube 116. At the same time, the ink supply pump 114 is operated to supply ink to the circulation path, and ink is discharged from the ejection port 120. In this manner, the recovery operation is reliably performed with the small amount of discharged ink.
FIG. 13 is a schematic view of a liquid jet head using an ink jet system described in JP 2003-182103 A. In this liquid jet head, ultraviolet-curable ink is used. A head portion 101 is heated up to a predetermined temperature by a heating unit 104. Accordingly, ink inside the head portion 101 is heated and the viscosity thereof is thereby reduced, and the viscosity-reduced ink is ejected from the head portion 101. The ink discharged from the head portion 101 flows through a second flow path 106, and then, by the pump 107, flows through a cooling unit 110, a connection portion 109, a first flow path 103, and into the upstream side of the heating unit 104. By operating the pump 107 with a valve 108 closed, ink is circulated inside the head portion 101. By opening the valve 108 when the operation of the pump 107 is stopped, ink is supplied from an ink tank 102 to the head portion 101 via the first flow path 103 due to water head difference.
In the ink circulation system described in JP 5-330073 A, ink is fed from the pump, which is placed near the ink tank, to the recording head unit via the outward ink tube, and returned from the recording head unit and then collected into the ink tank via the return ink tube. Therefore, it is necessary to connect both of the outward ink tube and the return ink tube to the ink tank. As a result, it takes time for assembly. Further, the outward ink tube and the return ink tube are made long. Furthermore, in the operation of the recording head unit, when the ink tubes are long, pressure fluctuation associated with the inertia of ink is likely to occur. As a result, it becomes difficult to control pressure at the ejection port.
In the ink circulation path described in JP 6-183024 A, when replenishing the ink supply tank, which is placed in the ink circulation path, with ink, it is necessary to first stop the circulation of ink, and then feed ink in the direction opposite to the circulation direction thereof by the recovery pump to thereby replenish the ink supply tank with ink from the main tank. In other words, it is not possible to replenish ink through the circulation path while performing an ejection operation from the recording head.
In the ink jet recording apparatus described in JP 9-104120 A, since the ink supply pump 114 is required in addition to the ink circulation pump 113, the number of pumps increases. Further, in the liquid jet head using an ink jet system described in JP 2003-182103 A, since ink is supplied on the basis of the difference in potential head between the head portion 101 and the surface of ink inside the ink tank 102, the ink tank 102 cannot be placed on an arbitrary position. Therefore, the locations of the head portion 101 and the ink tank 102 are limited, which causes inconvenience.